The invention relates to the processing or equalization of audio signals to compensate for deficiencies in the performance of the loudspeaker system. The previously recognized goal of "flat" response to a swept sine wave over the audible frequency range is approached in the prior art in two principal ways. Loudspeaker manufacturers employ elaborate crossover network circuitry to divide the signal among drivers whose design and composition are suited to relatively uniform performance with a frequency range. "Graphic" equalizers are introduced into the reproduction system to correct the signal for the variable influence of the listening room in different frequency ranges and to further compensate for speaker deficiencies, again with the goal of uniform response to a signal of a given amplitude whose frequency is varied. Lacking however has been a recognition that true rendition of a complex signal requires not only uniform frequency response at any given amplitude, but also uniform efficiency at different amplitudes of the same or other frequencies, and the maintenance of that uniformity as the delivery of one signal component of a given frequency and amplitude affects the efficiency of the driver in the simultaneous delivery of other amplitude and frequency components of a complex audio signal. FIG. 1 shows a hypothetical set of reponse curves at various amplitudes within the range of a single driver. Any one of the curves would be considered acceptably "flat" for commercial purposes within the prior art. However, unless the efficiency of the driver at points (A) and (B) is identical, undesirable coloration of the signal will result. If a musical instrument produces a primary tone of 1000 HZ at power level w.sub.1 after amplification, (A), and a harmonic overtone of 10 KHZ at w.sub.5, also after amplification, (B), faithful rendition of the tonal quality of the instrument is not assured by the flatness of the response curves at w.sub.1 and w.sub.5, but only by the equivalence of the response at the frequency and amplitude conditions (A) and (B). Moreover, such equivalence must be maintained as the driver attempts to render the separate signal components simultaneously. The efficiency of delivery of a weak higher frequency signal component will vary as lower frequency components are added and as their amplitudes are increased. Conventional equalizers, whose parameters are fixed by testing frequencies in isolation or with "white" noise, and only as affected by room conditions, cannot compensate for either of the above variations in speaker efficiency. Conventional equalizers fail because they bias a given frequency range by a fixed proportion regardless of the presence of signal components of other amplitudes and frequencies. Biasing in this fashion does not even compensate for room conditions appropriately as disclosed in U.S. Pat. No. 4,458,362, and it is not suitable for correction of speaker efficiency in any case. The invention, in either embodiment, samples the signal continuously, identifies the frequency and amplitude components, and modifies the signal only as appropriate under those conditions. For example, a relatively high frequency sub-range might receive enhancement only when it is below a given amplitude or only when it is rendered in combination with a much greater signal in a nearby frequency sub-range.